Results: All plant traits were genetically variable; directional selection favoured resistance to herbivory, latex production and the nitrogen content of leaves. Trichomes and latex were each negatively genetically correlated with abundances of herbivores, but not with herbivore damage; cardenolides and induced plant resistance were negatively genetically correlated with growth of monarchs.

Conclusion: Selection for plant defence was influenced by: (1) genetic correlations in plant susceptibility to multiple herbivores; (2) resistance traits affecting some, but not all, aspects of the insect community; and (3) early season herbivory inducing changes in milkweed influencing later season herbivores.

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